System and method for voltage and current sensing

ABSTRACT

In accordance with one aspect of the present disclosure, a current sensor configured to measure an AC current of a first conductor includes an outer coil having a first portion and a second portion. Each of the first and second portions are disposed about the first conductor passing through a center of the outer coil. The current sensor further includes an inner conductor disposed within the first and second portions of the outer coil and connected to each of the first and second portions of the outer coil.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority to U.S.Provisional Application Ser. No. 61/738,074, filed on Dec. 17, 2012, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrosurgical system and methodfor operating an electrosurgical generator. More particularly, thepresent disclosure relates to a system and method for measuring outputradio frequency (RF) voltage and current in an electrosurgicalgenerator.

2. Background of Related Art

Electrosurgery involves application of high radio frequency (RF)electrical energy to a surgical site to cut, ablate, or coagulatetissue. During treatment, the surgeon selects the desired tissue effectby setting controls on an electrosurgical generator and brings anelectrosurgical instrument (e.g., monopolar, bipolar, etc.) into contactwith the surgical site such that the instrument applies electrosurgicalenergy to the tissue.

Electrosurgical energy outputted by the generator has a predeterminedvoltage and current. The generator may also be configured to modifyproperties of the voltage and current waveforms, such as amplitude,phase, and duration to achieve as desired tissue effect, such as,cutting, ablation, coagulation, vessel sealing, and combinationsthereof.

The generator may also include voltage and current sensors formonitoring the voltage and current at the surgical site. The generatorutilizes the sensor readings to adjust the energy delivered to thesurgical site so that it matches the settings inputted by the surgeon.

Existing electrosurgical generators include transformers having a highpermeability material (e.g., ferrite) to sense the voltage and currentof the electrosurgical energy and isolate the patient. A limitation ofthe high permeability material is that the output of the transformers isnon-linear, fluctuates with temperature, and tolerances of thetransformers are not well-controlled. These limitations cause the sensedsignals to be less accurate than desired. Thus, there is a need for animprovement in the electrosurgical sensors.

SUMMARY

In accordance with one aspect of the present disclosure, a currentsensor configured to measure an AC current of a first conductor includesan outer coil having a first portion and a second portion. Each of thefirst and second portions are disposed about the first conductor passingthrough a center of the outer coil. The current sensor further includesan inner conductor disposed within the first and second portions of theouter coil and connected to each of the first and second portions of theouter coil.

According to aspects of the present disclosure, the current sensor mayfurther include a conditioning circuit having a first connector coupledto the first portion of the outer coil and a second connector coupled tothe second portion of the outer coil. The conditioning circuit isfurther configured to amplify and integrate a voltage received from thefirst and second connections and to output a measured AC current of thefirst conductor.

According to aspects of the present disclosure, the first and secondportions are separated by a gap which and the inner conductor comprisesa connector connecting the inner conductor to ground, such that the gapand the connector define an axis and the current sensor is symmetricalabout the axis.

According to other aspects of the present disclosure, the innerconductor may be connected to ground at approximately 0° relative to thelocations of the first and second connections along the axis.

According to aspects of the present disclosure, the current sensor mayhave an inductance at the outer coil is equal to about half of theinductance of the outer coil.

According to other aspects of the present disclosure, the innerconductor may be connected to a second end of the first portion of theouter coil approximately 180° relative to the locations of the first andsecond connections along the axis.

According to aspects of the present disclosure, the inner conductor maybe connected to a second end of the second portion of the outer coilapproximately 180° relative to the locations of the first and secondconnections along the axis.

According to other aspects of the present disclosure, the conditioningcircuit may include a differential amplifier including a first inputconfigured to connect to the first connection and a second inputconfigured to connect to the second connection.

According to aspects of the present disclosure, the first and secondgenerate a fourth voltage.

According to aspects of the present disclosure, the differentialamplifier removes the fourth voltage as the voltage from the firstconnection is common to the voltage of the second connection.

According to other aspects of the present disclosure, the conditioningcircuit may further include at least one filter connected to at leastone of the differential amplifier or the first and second connections.

According to aspects of the present disclosure, the first secondportions of the outer coil may be configured as a single coil with acenter tap configured to connect the inner conductor to the outer coil.

According to yet another aspect of the present disclosure, anelectrosurgical generator may include a radio frequency output stageconfigured to output at least one radio frequency waveform through anactive lead, and a current sensor coupled to the output stage andconfigured to output a first differentiated signal corresponding to acurrent of the at least one radio frequency waveform. The current sensorcoupled to a first conditioning circuit configured to integrate thefirst differentiated signal to output a processed current signalindicative of the current, and the current sensor is symmetrical about ahorizontal line. The current sensor includes an outer coil, whichincludes a first portion and a second portion, and each of the first andsecond portions form half of a toroid about the active lead, which isdisposed through a center of the outer coil. The current sensor furtherincludes an inner conductor disposed within the first and secondportions of the outer coil. Also, the electrosurgical generator includesa voltage sensor coupled to the output stage and configured to output asecond differentiated signal corresponding to a voltage of the at leastone radio frequency waveform. The voltage sensor is coupled to a secondconditioning circuit configured to integrate the second differentiatedsignal to output a processed voltage signal indicative of the voltage,and the first and second conditioning circuit have a substantiallysimilar bandpass and phase response.

According to a further aspect of the present disclosure, the outer coiland the inner conductor may be disposed on a printed circuit board withthe active lead passing through the outer coil.

According to another aspect of the present disclosure, the printedcircuit board may include outer conductive traces coupled around theactive lead, the outer conductive traces interconnected by at least onevia through the printed circuit board.

According to a further aspect of the present disclosure, the outer coilmay include a plurality of top conductive traces disposed on a topdielectric layer of the printed circuit board, and a plurality of bottomconductive traces disposed on a bottom dielectric layer of the printedcircuit board. The outer conductive traces are disposed over the bottomand top dielectric layers. The outer coil may include a plurality ofinner and outer vias interconnecting the pluralities of top and bottomconductive traces to form the outer coil.

According to a further aspect of the present disclosure, the innerconductor may include at least one conductive trace disposed within theouter coil and printed on an intermediate dielectric layer between thetop and bottom dielectric layers of the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a schematic block diagram of an embodiment of anelectrosurgical system according to the present disclosure;

FIG. 2 is a front view of an electrosurgical generator according to thepresent disclosure;

FIG. 3 is a schematic block diagram of the electrosurgical generator ofFIG. 2 according to the present disclosure;

FIG. 4 is a schematic diagram of a current sensor according to thepresent disclosure;

FIG. 5 is a partially-exposed, isometric view of a Rogowski coildisposed on a printed circuit board according to the present disclosure;

FIG. 6 is a partially-exposed, plan view of the Rogowski coil of FIG. 5according to the present disclosure;

FIG. 7 is an enlarged schematic view of the Rogowski coil of FIG. 5according to the present disclosure;

FIG. 8 is a side, cross-sectional view of the printed circuit board ofFIG. 5 according to the present disclosure;

FIG. 9 is a plan view of the printed circuit board of FIG. 5 accordingto the present disclosure;

FIG. 10A is a plan view of a Rogowski coil disposed on a printed circuitboard according to the present disclosure;

FIG. 10B is a side, cross-sectional view taken along 10B-10B of theRogowski coil disposed on the printed circuit board according to thepresent disclosure;

FIG. 11 is a schematic circuit diagram of a gain amplifier according tothe present disclosure;

FIG. 12 is a schematic circuit diagram of a single-ended amplifieraccording to the present disclosure;

FIG. 13 is a schematic circuit diagram of a high-pass filter accordingto the present disclosure;

FIG. 14 is a schematic circuit diagram of a low-pass filter according tothe present disclosure;

FIG. 15 is a schematic circuit diagram of an integrator according to thepresent disclosure;

FIG. 16 is a plot of a bandwidth of the current sensor according to thepresent disclosure;

FIG. 17 is a schematic diagram of a voltage sensor according to thepresent disclosure;

FIG. 18 is a plan, cross-sectional view of the voltage sensor accordingto the present disclosure;

FIG. 19A is a schematic diagram of a Rogowski coil according to thepresent disclosure;

FIG. 19B is a schematic diagram of a symmetric Rogowski coil accordingto the present disclosure;

FIG. 20 is a top view of a symmetric Rogowski coil disposed on a printedcircuit board according to the present disclosure; and

FIG. 21 is a top view of an alternative symmetric Rogowski coil disposedon a printed circuit board according to the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail.

The present disclosure provides a current sensor configured to measurean AC current of a first conductor. The current sensor includes an outercoil with a first portion and a second portion. Each of the first andsecond portions form half of a toroid about the first conductor and thefirst conductor is disposed through a center of the outer coil. Thecurrent sensor includes an inner conductor disposed within the first andsecond portions of the outer coil, and a conditioning circuit. Theconditioning circuit includes a first connector coupled to the firstportion of the outer coil and a second connector coupled to the secondportion of the outer coil, and the conditioning circuit is configured toamplify and integrate a voltage received from the first and secondconnections and to output a measured AC current of the first conductor.

A generator according to the present disclosure can perform monopolarand/or bipolar electrosurgical procedures, including vessel sealingprocedures. The generator may include a plurality of outputs forinterfacing with various electrosurgical instruments (e.g., a monopolarinstrument, return electrode, bipolar electrosurgical forceps,footswitch, etc.). Further, the generator includes electronic circuitryconfigured to generate radio frequency energy specifically suited forvarious electrosurgical modes (e.g., cutting, blending, division, etc.)and procedures (e.g., monopolar, bipolar, vessel sealing). Inembodiments, the generator may be embedded, integrated or otherwisecoupled to the electrosurgical instruments providing for an all-in-oneelectrosurgical apparatus.

FIG. 1 is a schematic illustration of a bipolar and monopolarelectrosurgical system 1 according to the present disclosure. The system1 may include one or more monopolar electrosurgical instruments 2 havingone or more electrodes (e.g., electrosurgical cutting probe, ablationelectrode(s), etc.) for treating tissue of a patient. Electrosurgicalenergy is supplied to the instrument 2 by a generator 200 via a supplyline 4 that is connected to an active terminal 230 (FIG. 3) of thegenerator 200, allowing the instrument 2 to coagulate, ablate and/orotherwise treat tissue. The energy is returned to the generator 200through a return electrode 6 via a return line 8 at a return terminal232 (FIG. 3) of the generator 200. The system 1 may include a pluralityof return electrodes 6 that are disposed on a patient to minimize thechances of tissue damage by maximizing the overall contact area with thepatient. In addition, the generator 200 and the return electrode 6 maybe configured for monitoring so-called “tissue-to-patient” contact toinsure that sufficient contact exists therebetween to further minimizechances of tissue damage.

The system 1 may also include a bipolar electrosurgical forceps 10having one or more electrodes for treating tissue of a patient. Theelectrosurgical forceps 10 includes a housing 11 and opposing jawmembers 13 and 15 disposed at a distal end of a shaft 12. The jawmembers 13 and 15 have one or more active electrodes 14 and a returnelectrode 16 disposed therein, respectively. The active electrode 14 andthe return electrode 16 are connected to the generator 200 through cable18 that includes the supply and return lines 4, 8 coupled to the activeand return terminals 230, 232, respectively (FIG. 3). Theelectrosurgical forceps 10 is coupled to the generator 200 at aconnector having connections to the active and return terminals 230 and232 (e.g., pins) via a plug disposed at the end of the cable 18, whereinthe plug includes contacts from the supply and return lines 4, 8 asdiscussed in more detail below.

With reference to FIG. 2, a front face 240 of the generator 200 isshown. The generator 200 may be any suitable type (e.g.,electrosurgical, microwave, etc.) and may include a plurality ofconnectors 250-262 to accommodate various types of electrosurgicalinstruments (e.g., electrosurgical forceps 10, etc.). The connectors250-262 may include various detection devices that can read (e.g., scan,decode, etc.) identifying information encoded or otherwise recorded onor within the plugs or cables of the instruments. The connectors 250-262are configured to decode the information encoded on the plugscorresponding to the operating parameters of particular instrumentsallowing the generator 200 to preset energy delivery settings based onthe connected instrument. In embodiments, data may be encoded in barcodes, electrical components (e.g., resistors, capacitors, etc.), RFIDchips, magnets, non-transitory storage (e.g., non-volatile memory,EEPROM, etc.), which may then be coupled to or integrated into the plug.Corresponding detection devices may include, but are not limited to, barcode readers, electrical sensors, RFID readers, Hall Effect sensors,memory readers, etc. and any other suitable decoders configured todecode data.

The generator 200 includes one or more display screens 242, 244, 246 forproviding the user with variety of output information (e.g., intensitysettings, treatment complete indicators, etc.). Each of the screens 242,244, 246 is associated with corresponding connector 250-262. Thegenerator 200 includes suitable input controls (e.g., buttons,activators, switches, touch screen, etc.) for controlling the generator200. The display screens 242, 244, 246 are also configured as touchscreens that display a corresponding menu for the electrosurgicalinstruments (e.g., electrosurgical forceps 10, etc.). The user thenmakes inputs by simply touching corresponding menu options.

Screen 242 controls monopolar output and the devices connected to theconnectors 250 and 252. Connector 250 is configured to couple tomonopolar electrosurgical instrument (e.g., electrosurgical pencil) andconnector 252 is configured to couple to a foot switch (not shown). Thefoot switch provides for additional inputs (e.g., replicating inputs ofthe generator 200). Screen 244 controls monopolar and bipolar output andthe devices connected to the connectors 256 and 258. Connector 256 isconfigured to couple to other monopolar instruments. Connector 258 isconfigured to couple to a bipolar instrument (not shown).

Screen 246 controls bipolar sealing procedures performed by the forceps10 that may be plugged into the connectors 260 and 262. The generator200 outputs energy through the connectors 260 and 262 suitable forsealing tissue grasped by the forceps 10. In particular, screen 246outputs a user interface that allows the user to input a user-definedintensity setting. The user-defined setting may be any setting thatallows the user to adjust one or more energy delivery parameters, suchas power, current, voltage, energy, etc. or sealing parameters, such aspressure, sealing duration, etc. The user-defined setting is transmittedto the controller 224 where the setting may be saved in memory 226. Inembodiments, the intensity setting may be a number scale, such as fromone to ten or one to five. In embodiments, the intensity setting may beassociated with an output curve of the generator 200. The intensitysettings may be specific for each forceps 10 being utilized, such thatvarious instruments provide the user with a specific intensity scalecorresponding to the forceps 10.

FIG. 3 shows a schematic block diagram of the generator 200 configuredto output electrosurgical energy. The generator 200 includes acontroller 224, a power supply 227, and an output stage 228. The powersupply 227 may be a direct current high voltage power supply and thatconnects to an AC source (e.g., line voltage) and provides high voltageDC power to an output stage 228, which then converts high voltage DCpower into treatment energy (e.g., ultrasonic, electrosurgical ormicrowave) and delivers the energy to the active terminal 230. Theenergy is returned thereto via the return terminal 232. The output stage228 is configured to operate in a plurality of modes, during which thegenerator 200 outputs corresponding waveforms having specific dutycycles, peak voltages, crest factors, etc. In another embodiment, thegenerator 200 may be based on other types of suitable power supplytopologies.

The controller 224 includes a microprocessor 225 operably connected to amemory 226, which may include transitory type memory (e.g., RAM) and/ornon-transitory type memory (e.g., flash media, disk media, etc.). Themicroprocessor 225 includes an output port that is operably connected tothe power supply 227 and/or output stage 228 allowing the microprocessor225 to control the output of the generator 200 according to either openand/or closed control loop schemes. Those skilled in the art willappreciate that the microprocessor 225 may be substituted by any logicprocessor (e.g., control circuit) adapted to perform the calculationsand/or set of instructions discussed herein.

A closed loop control scheme is a feedback control loop, in which aplurality of sensors measure a variety of tissue and energy properties(e.g., tissue impedance, tissue temperature, output power, currentand/or voltage, etc.), and provide feedback to the controller 224. Thecontroller 224 then signals the power supply 227 and/or output stage228, which then adjusts the DC and/or power supply, respectively. Thecontroller 224 also receives input signals from the input controls ofthe generator 200, the instrument 2 and/or forceps 10, as describedabove. The controller 224 utilizes the input signals to adjust poweroutputted by the generator 200 in the closed control loop and/orperforms other control functions thereon.

The generator 200 according to the present disclosure includes an RFcurrent sensor 300 and an RF voltage sensor 600. The RF current sensor300 is coupled to the active terminal 230 and provides measurements ofthe RF current supplied by the output stage 228. The RF voltage sensor600 is coupled to the active and return terminals 230 and 232 providesmeasurements of the RF voltage supplied by the output stage 228. Inembodiments, the RF current and voltage sensors 300 and 600 may becoupled to active and return leads 228 a and 228 b, which interconnectthe active and return terminals 230 and 232 to the output stage 228,respectively. The RF current and voltage sensors 300 and 600 provide thesensed RF voltage and current signals, respectively, to the controller224, which then may adjust output of the power supply 227 and/or theoutput stage 228 in response to the sensed RF voltage and currentsignals. Various components of the generator 200, namely, the outputstage 228, the RF current and voltage sensors 300 and 600, may bedisposed on a printed circuit board (PCB).

Transformers are conventionally used as current and voltage sensors asthey provide a required patient isolation. However, transformers providefluctuating readings due to temperature, signal amplitude, etc. Thismakes accurate readings difficult with respect to phase andgain-bandwidth of the sensor signals. As a result, the signals need tobe post-processed to arrive at accurate signals. The present disclosureprovides for novel RF voltage and current sensors 300 and 600 whichovercome the problems of conventional sensors.

FIG. 4 shows the RF current sensor 300 which includes a Rogowski coil302. As used herein, the term “Rogowski coil” refers to an electricaldevice for measuring alternating current (e.g., RF current) and includesan outer conductor coil (e.g., toroid) that acts as an active conductorwrapped around an inner conductor, a so-called “Bucking coil” that actsas a return conductor with a lead carrying the current passing throughthe center of the coil. The coil may have any suitable shape such ashelical, toroidal, etc. In embodiments, the coil may have a polygonalcross-section. The Rogowski coil may include a low permeability core(e.g., air core) and provides a voltage output having a time-derivate ofthe current being measured to a conditioning circuit that integrates theoutput to provide a voltage signal indicative of the current. Inembodiments, the Rogowski coil 302 may be implemented on a printedcircuit board and may include a gap so that the Rogowski coil 302 may bewrapped about the conductor carrying the current to be measured.

As described in greater detail below, the Rogowski coil 302 of thepresent disclosure increases common mode voltage rejection due to theconnection of the Bucking coil. Further, the conditioning circuit 301according to the present disclosure is configured as a differentialamplifier that improves the common-mode rejection ratio (CMRR) unlikeprior art conditioning circuits which are usually single ended and thus,fail to increase CMRR.

The Rogowski coil 302 is coupled to a conditioning circuit 301 having aresistor divider 304, which includes resistors 304 a and 304 b. Inembodiments, the conditioning circuit 301 may be implemented as anyintegrator (e.g., logic processor) or differential amplifier. Theresistor divider 304 removes resonance of the coil 302 at its resonantfrequency. As described in further details below with respect to FIGS.5-9, the Rogowski coil 302 is disposed about the active lead 228 a, thecoil 302 is configured to measure the current passing therethrough as avoltage signal. The voltage signal from the coil 302 is then supplied toan optional gain amplifier 306 which increases the amplitude of thevoltage signal. The gain amplifier 306 or the coil 302, if the gainamplifier 306 is not used, is also coupled to a single-ended amplifier308, which is in turn, coupled to a bandpass filter 310. The singleended amplifier 308 is a differential-to-single-ended converter whosefunction is to convert the differential signal from the coil 302 to asingle-ended signal. The amplifier 308 may have a monolithicconfiguration that provides improved common mode rejection.

The bandpass filter 310 removes higher and lower frequency components ofthe voltage signal which is then transmitted to an integrator 312. Sincethe voltage that is induced in the Rogowski coil 302 is proportional tothe rate of change of current that is flowing through the active leads228 a the integrator 312 is utilized to provide an output voltage signalthat is proportional to the current.

In embodiments, the integrator 312 may be coupled to switchableattenuation circuit 314, which may include one or more actively switchedcomponents. The attenuation circuit 314 may then be coupled toadditional components such as an offset circuit 316, analog-digitalconverters, and the like prior to supplying the signal to the controller224.

FIGS. 5-9 show the Rogowski coil 302 according to the presentdisclosure. The coil 302 has substantially a circular shape having anopening therethrough defined by inner circumferential region 302 a (FIG.6). The lead 228 a is disposed through the opening 301 allowing the coil302 to measure the current flow through the lead 228 a.

As shown in FIGS. 5 and 6, the coil 302 has a substantially toroidalshape and is formed on a printed circuit board (PCB) 400 and includesand inner circumferential region 302 a and an outer circumferentialregion 302 b (FIG. 6). The coil 302 includes forming an inner portion(“Bucking coil”) 405 of the coil 302 and an outer coil 407. Inembodiments, the coil 302 may have any other suitable shape (e.g.,having a polygonal cross-section) with the outer coil 407 wrapped aboutthe inner portion 405 and defining an opening therethrough. Inembodiments, the coil 302 may be a coil-wrapped phenolic toroid having alow permeability (μ₀).

The current i(t) flowing through lead 228 a produces a first magneticfield proportional to the rate of change of the sensed current i(t). Theouter coil 407 detects the first magnetic field and produces a firstvoltage corresponding to the first magnetic field (e.g., field 1905 ofFIGS. 19A-B). The outer coil 407 also detects a second magnetic fieldand produces a second voltage corresponding to the second magnetic field(e.g., field 1930 of FIGS. 19A-B). The second magnetic field isorthogonal to the first magnetic field and is not related to the sensedcurrent. The inner portion 405 senses the second magnetic field andproduces a third voltage proportional to the second magnetic field. Thesecond voltage and third voltage produced have approximately the samemagnitude and connected so that the cancel each other and are furtherremoved through conditioning circuit 301.

The PCB 400 may be a multilayer PCB formed from any suitable dielectricmaterial, including, but not limited to composite materials composed ofwoven fiberglass cloth with an epoxy resin binder such as FR-4. As shownin FIG. 8, the PCB 400 includes a first or top layer 404 a and a bottomlayer 404 e of sufficient thickness to prevent capacitive couplingbetween conductive traces 408 b and 408 e. The active lead 228 a iscoupled to conductive traces 408 a and 408 f, respectively, which aredisposed over the top and bottom layers 404 a and 404 e as shown inFIGS. 8 and 9. The active leads 228 a may be coupled to a patient sideconnector 420 disposed on the PCB 400 as shown in FIG. 9. The traces 408a and 408 f are interconnected through the center 301 via one or morevias 409 a, which pass through the entire PCB 400 (e.g., layers 404a-404 e).

The outer coil 407 includes a top trace 408 b disposed between the toplayer 404 a and an intermediate layer 404 b of the PCB 400. The outercoil 407 also includes a bottom trace 408 e disposed between the bottomlayer 404 e and an intermediate layer 404 d of the PCB 400. The traces408 b and 408 e are interconnected by a plurality of inner vias 409 band outer vias 409 c. The layers 404 a and 404 e insulate the coil 302(e.g., outer coil 407) conductive traces 408 a and 408 f and provide anisolation barrier between the patient and the generator 200.

As shown in FIGS. 5-7, the inner vias 409 b are arranged to form theinner circumferential region 302 a of the coil 302 and the outer vias409 c form the outer circumferential region 302 b of the coil 302. Theinner and outer vias 409 b and 409 c pass through the layers 404 b, 404c, and 404 d. The inner vias 409 b and outer vias 409 c may be disposeda concentric configuration as shown in FIGS. 10A and 10B, respectively.In a concentric configuration, corresponding inner and outer vias 409 band 409 c lie along same rays. In a staggered configuration, the innerand outer vias 409 b and 409 c lie along alternating rays “r” as shownin FIGS. 5-7. The rays “r” are disposed at and an angle “α” relative toeach other and the inner vias 409 b are separated by a distance “d.”Each of the inner vias 409 b is connected to two neighboring outer vias409 c through traces 408 a and 408 e and vice versa. The interconnectionof the vias 409 b and 409 c with the traces 408 a and 408 e forms aplurality of loops, which in turn, form the outer coil 407 as shown inFIG. 5.

The outer coil 407 may include any suitable number of turns, inembodiments from about 50 turns to about 100 turns. The maximum numberof turns depends on the radius of the inner circumferential region 302a, via aspect ratio, thickness of the outer coil 407 and/or PCB 400, andspacing between the turns based on the limits of manufacturability ofthe PCB material (e.g., trace to trace, trace to via, via annular paddimension, anything that may limit the placement of the conductors onthe PCB).

With reference to FIGS. 6 and 8, the inner portion 405 is disposedwithin the outer coil 407 and also has a substantially circular shape.The inner portion 405 may include an upper trace 408 c and a bottomtrace 408 d. The traces 408 c and 408 d are disposed over a dielectriclayer 404 c, such that the traces 408 c and 408 d are insulated fromeach other. The traces 408 c and 408 d may be electrically coupled toeach other. In embodiments, the inner portion 405 may be formed from asingle trace.

As shown in FIGS. 6 and 9, the coil 302 is coupled to the othercomponents of the sensor 300 at a side connector 422, which may alsodisposed on the PCB 400. The coil 302 includes a first terminal 410 acoupled to the inner portion 405 and a second terminal 410 b coupled tothe outer coil 407. In particular, the outer coil 407 is disposed overthe inner portion 405 and is coupled thereto. Thus, two terminals 410 aand 410 b are disposed at one end of the coil 302. The interconnectionbetween the inner portion 405 and the outer portion 407 as well as theconnection to the terminals 410 a and 410 b may be made through the vias409 b and 409 c.

The controller 224 is provided voltage signals from the sensor 300,which are then utilized to determine the current. Various formulas maybe utilized by the controller 224 to determine the current. The voltageproduced by the coil 302 may be calculated using the formula (I):

$\begin{matrix}{V_{OUT} = {\frac{{- A_{LOOP}}N_{LOOPS}}{2\pi \; R_{COIL}}\mu_{0}\frac{I}{t}}} & (I)\end{matrix}$

In formula (I), A is the area of the turn (e.g., loop) formed by thevias 409 b and 409 c with the traces 408 a and 408 b, N is the number ofturns, R is the major radius of the coil 302, μ₀ is the magneticconstant, dI/dt is the rate of change of the current being measured bythe coil 302.

Inductance and capacitance of the coil may be calculated using theformulae (II)-(IV), respectively. Capacitance of the coil 302 is used todetermine self-resonance and may be calculated using parallel-wire modelformulae, namely, capacitances of inner and outer vias 409 b and 409 cand traces 408 a and 408 b.

$\begin{matrix}{L_{Coil} = {\frac{\mu_{0} \cdot N_{Turns}^{2} \cdot t_{coil}}{2\pi}{\ln \left( \frac{r_{{coil}\; \_ \; {inner}} + w_{coil}}{r_{{coil}\; \_ \; {inner}}} \right)}}} & ({II}) \\{C_{coil} = {N_{turns} \cdot \left( {{2 \cdot C_{{trace} - {trace}}} + C_{{via} - {inner}} + C_{{via} - {outer}}} \right)}} & ({III}) \\{C_{} = \frac{\pi \cdot ɛ_{0} \cdot ɛ_{r} \cdot l_{{trace}/{via}}}{\ln \left( {\frac{d_{{between}\; \_ \; {{trace}/{via}}}}{2 \cdot r_{{via}/{trace}}} + \sqrt{\frac{d_{\;_{{between}\; \_ \; {{trace}/{via}}}}^{2}}{r_{{via}/{trace}}^{2}} - 1}} \right)}} & ({IV})\end{matrix}$

In formulae (II)-(IV), in addition to the variable and constantsutilized in formula (I), t is thickness (e.g., distance betweenconductive traces 408 b and 408 e), r is radius, w is the radialdistance between inner and outer circumferential regions 302 a and 302b, Rcoil_inner is the radial distance to the inner circumferentialregion 302 a, l is length, ∈₀ is vacuum permittivity constant, and ∈_(r)is the dielectric constant of the PCB.

FIGS. 10A and 10B show another embodiment of a Rogowski coil 552. Thecoil 552 is substantially similar to the coil 302. The coil 552 is alsocoupled to the conditioning circuit 301, which is disposed on the PCB400. In this embodiment, the coil 552 is formed within the PCB 400 andthe lead 228 a may pass directly through the coil 552. The PCB 400includes one or more openings 556 a and 556 b, with the opening 556 apassing through an opening 558 defined within the coil 552. The leads228 a may be wound about a spacer 554, which is disposed between theopenings 556 a and 556 b, which aligns the leads 228 a for passagethrough the coil 552. The coil 552 operates in the same manner asdescribed above with respect to the coil 302 by sensing the currentpassing through the leads 228 a. The leads 228 a may be wrapped around aspacer 554 disposed between the openings 556 a and 556 b, which alignsthe leads 228 a for passage through the coil 552. The spacer 554 mayinclude an upper portion 554 a and a lower portion 554 b disposed oneach side of the PCB 400.

With reference to FIGS. 4 and 1115, conditioning circuit 301 of thesensor 300 is shown. Since the coil 302 provides a differentiatingresponse, the output must be integrated to provide the actual responsevia the conditioning circuit 301 of the sensor 300. The output of thecoil 302 is integrated to produce a signal that is proportional to thecurrent in the active lead 228 a. The conditioning circuit 301 providesthat integration with the integrator 312. This allows for easyadjustability of the sensor gain. Gain may be set by adjusting thefrequency setpoint of the integrator 312. The setpoint may be achievedby selection of hardware component values (e.g., discrete resistor orcapacitor substitution), selection of software values (e.g., digital oranalog potentiometers or adjustable capacitors), including programmablegain amplifiers as described in detail below, or combinations thereof.

The gain amplifier 306 of the conditioning circuit 301 is shown in FIG.11 and includes a pair of operation amplifiers 306 a and 306 bconfigured to provide differential gain without adding to thecommon-mode gain. The voltage signal from the coil 302 is provided tothe positive terminals of the amplifiers 306 a and 306 b. The outputs ofthe amplifiers 306 a are interconnected by a voltage divider network 306c including three resistors 306 d, 306 e, 306 f. Terminal resistors 306d and 306 f are coupled in parallel with capacitors 306 g and 306 h,respectively. The signal from the parallel circuits is coupled to thenegative terminals of the amplifiers 306 a and 306 b, which provideclosed-loop feedback thereto. These capacitors 306 g and 306 h provideamplifier stabilization and may also provide for the integration of thesignal.

The output of each of the operational amplifiers 306 a and 306 b isprovided to the single-ended amplifier 308, which is shown in FIG. 12.In particular, the output of the amplifiers 306 a and 306 b is suppliedto the positive and negative inputs of the amplifier 308. The amplifier308 combines the output of the amplifiers 306 a and 306 b to provide asingle output to the bandpass filter 310. The amplifier 308 includes aclosed feedback circuit having a reference signal connected to groundincluding a resistor 308 a which is connected in parallel with acapacitor 308 b and in series with a resistor 308 c. The parallelcircuit provides a feedback signal to a feedback input and the seriescircuit provides a reference signal to a reference input of theamplifier 308.

The bandpass filter 310 includes a high-pass filter 309 and a low-passfilter 311 as shown in FIGS. 13 and 14, respectively. In embodiments,the output from the amplifier 308 may be passed through the high-passfilter 309 before being passed through the low-pass filter 311, or viceversa.

The high-pass filter 309 is configured to pass high frequencies andattenuate lower frequencies. The high-pass filter 309 includes anoperational amplifier 309 a. The input from the amplifier 308 or thelow-pass filter 311 is provided to the positive input of the amplifier309 a having a first capacitor 309 b coupled in series with a secondcapacitor 309 c and a first resistor 309 d and a second resistor 309 e.The negative input of the amplifier 309 a is provided by a feedback loopfrom a third resistor 309 f coupled in series with a grounded fourthresistor 309 g.

The low-pass filter 311 is configured to pass high frequencies andattenuates lower frequencies. The low-pass filter 311 includes anoperational amplifier 311 a. The input from the amplifier 308 or thehigh-pass filter 309 is provided to the positive input of the amplifier311 a having a first resistor 311 b coupled in series with a secondresistor 311 c and a first capacitor 311 d and a second capacitor 311 e.The negative input of the amplifier 311 a is provided by a feedback loopfrom a third resistor 311 f coupled in series with a grounded fourthresistor 311 g.

Since the voltage that is induced in the Rogowski coil 302 isproportional to the rate of change of current that is flowing throughthe active leads 228 a the integrator 312 is utilized to provide anoutput voltage signal that is proportional to the current. Inembodiments, a leaky integrator may be used. As used herein the term“leaky integrator” refers to an integrator having a low-pass filter asdescribed in further detail below with respect to FIG. 14. Theintegrator 312 includes an amplifier 312 a with a positive input thereofcoupled to a ground. The input from the bandpass filter 310 is fedthrough a low-pass filter 312 b, which includes a first resistor 312 ccoupled in series with a second resistor 312 d that is coupled inparallel with a capacitor 312 e. The second resistor 312 d and thecapacitor 312 e are also coupled to the output of the amplifier 312 athereby providing a closed loop feedback thereto. The input signal isthen fed to the negative input of the amplifier 312 a. The filter 312 bmay be used in lieu of or in combination with the bandpass filter 310.

The integrator 312 provides a negative slope of voltage gain versesfrequency. This compensates, or flattens the opposite slope of thesignal coming from the coil 302. Further, the integrator 312 hasextremely high DC gain. The frequency band of interest for the generator200 is well above DC. The integrator gain would create problems if a DCoffset were present at its input. The high-pass portion of the band-passfilter 310 reduces the low frequency components and reduces any DCoffset, which mitigates issues caused by the integrator's amplificationof these components.

FIG. 16 shows a graph 500 illustrating individual gain response of thecoil 302, the integrator 312, and the combined response of the coil 302and the integrator 312. The graph 500 shows the overall response of thecoil 302 as a plot 502, the response of the integrator 312 as a plot504, and the combined response of the coil 302 and the integrator 312 ofthe sensor 300 as a plot 506, which is a combination of the plots 502and 504. Frequency, f1, is determined by the response of the integrator312 and frequency, f2, is determined by the resonant frequency of thecoil 302.

FIG. 17 shows the RF voltage sensor 600. The sensor 600 is configured asa capacitive divider 602 including first and second capacitors 602 a and602 b coupled to conditioning circuit 601. The conditioning circuit 601of the sensor 600 is substantially similar to the conditioning circuitof the sensor 300 and includes the same components, which are designatedusing like numerals. The capacitive divider 602 is coupled to a resistordivider 604 including first and second resistors 604 a and 604 b. Thevoltage is then supplied to an optional gain amplifier 606 whichincreases the amplitude of the voltage signal. The gain amplifier 606 orthe capacitive divider 602, if the gain amplifier 606 is not used, iscoupled to a single-ended amplifier 608, which is in turn, coupled to abandpass filter 610. The single ended amplifier 608 is adifferential-to-single-ended converter whose function is to convert thedifferential signal from the coil 602 to a single-ended signal. Theamplifier 608 may have a monolithic configuration that provides improvedcommon mode rejection.

The bandpass filter 610 removes higher and lower frequency components ofthe voltage signal which is then transmitted to an integrator 612. Sincethe voltage that is induced in the capacitive divider 602 isproportional to the rate of change of current that is flowing throughthe active and return leads 228 a and 228 b the integrator 612 isutilized to provide an output voltage signal that is proportional to thesensed RF voltage.

In embodiments, the integrator 612 may be coupled to switchableattenuation circuit 614, which may include one or more actively switchedcomponents. The attenuation circuit 614 may then be coupled toadditional components such as an offset circuit 616, analog-digitalconverters, and the like prior to supplying the signal to the controller224.

The capacitive divider 602 is shown in more detail in FIG. 18. Thecapacitors 602 a and 602 b are a matched pair of capacitors havingsubstantially similar dielectric properties. The capacitors 602 a and602 b may be plate capacitors that are disposed in a housing 560 aresecured therein via a potting material 562. Potting material 562 may beany suitable dielectric material that is injection molded or otherwiseprovided into the housing 560. The material 562 also provides additionalinsulation between the capacitors 602 a and 602 b. The capacitivedivider 602 may be disposed in proximity to the active and return leads228 a and 228 b allowing the capacitors to measure the voltagetherebetween.

The capacitors 602 a and 602 b are insulated from the active and returnleads 228 a and 228 b and provide an isolation barrier between thepatient and the generator 200. The capacitors 602 a and 602 b aredisposed in proximity to the active and return leads 228 a and 228 b,such that the voltage is capacitively detected by the capacitors 602 aand 602 b. In other words, the capacitors 602 a and 602 b arecapacitively coupled to the active and return leads 228 a and 228 b. Thecapacitors 602 a and 602 b may be plate capacitors, each having oneplace connected to the active and return leads 228 a and 228 b and theother plate connected to the conditioning circuit 601. In embodiments,the plates of the capacitors 602 a and 602 b may be disposed on opposingsides of a PCB. Thus, the material (e.g., PCB) between the platesprovides the insulation. As used herein the term “capacitively coupled”denotes indirect electrical contact between the capacitors 602 a and 602b and the active and return leads 228 a and 228 b, such that electricalcurrent passing through the return leads 228 a and 228 b is detectedthrough a dielectric.

The capacitor 602 a and the resistor 604 a as well as the capacitor 602b and the resistor 604 b combinations create similar voltage response asthe coil 302. Thus, matching the gain amplifier 606, the single-endedamplifier 608, the bandpass filter 610, and the integrator 612 to thegain amplifier 306, the single-ended amplifier 308, the bandpass filter310, and the integrator 312 allows for matching the bandpass (e.g.,gain) and phase response of the sensors 300 and 600. In embodiments, theconditioning circuits 300 and 600 may have a substantially similarbandpass and phase response. As used herein, the term “substantiallysimilar” denotes a difference between the bandpass and phase response ofthe conditioning circuits 300 and 600 of no more than from about 1degree difference between voltage and current channels to about 15degrees, in embodiments, from about 2 degrees to about 10 degrees, infurther embodiments about 5 degrees. Since the integration of bothcurrent and voltage sensors 300 and 600 may be performed by identicalconditioning circuit 301 and 601, the two signals are matched in gainand phase characteristics, which provides for accurate and preciserepresentation of real power dissipated by the tissue duringelectrosurgery.

The capacitors 602 a and 602 b block the RF voltage delivered to thepatient and provide a low sense voltage across the resistors 604 a and604 b. The differential gain of the conditioning capacitors 602 a and602 b is substantially equal to the common-mode gain due to closematching of the capacitor 602 a and the resistor 604 a as well as thecapacitor 602 b and the resistor 604 b combinations. Thus, thecommon-mode rejection ratio effectively is the common-mode rejectionratio of the conditioning circuit 601. As a result, if the capacitors602 a and 602 b and/or the resistors 604 a and 604 b are not matchedclosely, the common mode signal become a differential mode signalthereby generating an error signal.

The voltage and current sensors of the present disclosure providevarious improvements over transformers in terms of isolation. In theRogowski coil implementation the isolation and dielectric strength comefrom adequate wire insulation or adequate PCB material insulation. Asthese are inherent in the design and do not need to be applied manuallyas in a transformer implementation. This reduces the manufacturingcosts.

Similarly, the matching of the capacitors can be accomplished via theconstruction techniques of the PCB manufacture. This ensures veryclosely matched parts. In addition to excellent matching characteristicsthe dielectric strength is provided by the PCB manufacture. Thecapacitance is controlled very precisely in this instance and is muchlower than in the transformer implementation. These aspects areimportant for patient safety and improved operation of the sensors.

FIG. 19A shows a system 1935 of an embodiment of a Rogowski coil 1936surrounding the active lead 228 a that includes an AC current, currenti(t), passing through. The Rogowski coil 1936 includes an outer coil1901 wrapped around an inner conductor (“bucking coil”) 1902. The innerconductor 1902 and outer coil 1901 can be a single wire or conductor, ortwo conductors connected together at connection point 1906.

A current i(t) flowing through active lead 228 a produces a firstmagnetic field 1905 proportional to the rate of change of the sensedcurrent i(t). The outer coil 1901 detects the first magnetic field 1905and produces a first voltage corresponding to the first magnetic field.The outer coil 1901 also detects a second magnetic field 1930 andproduces a second voltage corresponding to the second magnetic field1930. The second magnetic field 1930 is orthogonal to the first magneticfield 1905 and is not related to the sensed current. The inner conductor1902 senses the second magnetic field 1930 and produces a third voltageproportional to the second magnetic field 1930. The second voltage andthird voltage have approximately the same magnitude and are reduced byconnecting the outer coil 1901 with the inner coil 1902 at theconnection point 1906 to attain the first voltage which is indicative ofthe current i(t).

The Rogowski coil 1936 is connected to conditioning circuitry 1975though connections 1909 and 1911. A first end of the outer coil 1901connects to a first input 1964 (positive input) of operational amplifier1960 through connection 1909. The first end of the outer coil 1901 isalso connected to a ground through connection 1913. Connection 1911connects a second end of the inner conductor 1902 (alternatively, asecond end of the outer coil when a single conductor is used) to asecond input 1962 (negative input) of the operational amplifier 1960 viaa first resistor 1950. The first resistor may be about 1 kilo ohms (kΩ)to about 1,000 kΩ. The operational amplifier 1960 amplifies the voltagefrom connections 1909 and 1911 to provide an output 1966. A filter 1972is connected in parallel to the operational amplifier 1960. The filter1972 may be an RC filter with resistor 1970 and capacitor 1980. Theresistor may be about 33 kΩ to about 3330 kΩ and the capacitor may befrom about 1 nano farad (nF) to about 100 nF.

The outer coil 1901 may include an air core or a core formed from anyother suitable dielectric material, which provides a low inductancewithin the coil. The inductance of the coil may be calculated usingformula II (described above). As the load impedances are in parallel,the impedance of the coil is the dominant impedance because the coil1936 has the lower impedance.

When active lead 228 a supplying a large voltage with a small current,an undesirable fourth voltage may be produced in the Rogowski coil 1936.The fourth voltage may come from a gap 1912 in Rogowski coil 1936 whichresults in an undesirable magnetic field in a region 1904 and/or fromdiscontinuities at connections 1906, 1909, and/or 1911. Fourth voltageis capacitively coupled from the active lead 228 a to any conductor inthe coil (e.g., connection 1911). If the coil is symmetrical then thevalue of coupling will be equal and thus canceled by the differentialamp.

FIG. 19B shows a system of a symmetric Rogowski coil 1900 surroundingactive lead 228 a. The symmetric Rogowski coil 1900 is symmetric aboutaxis X-X with an outer coil 1911 formed of a first portion 1911 a and asecond portion 1911 b disposed in each side of axis X-X. The firstportion 1911 a of the outer coil 1911 connects to conditioning circuitry1976 configured as a differential amplifier at a first connection 1945.The second portion 1911 b of the outer coil 1911 connects toconditioning circuitry 1976 at a second connection 1955.

An inner conductor 1920, also called a “bucking” coil, runs within theouter coil 1911. The inner conductor 1920 is connected to a ground 1990by a third connection 1940. A first end 1915 of inner conductor 1920 isconnected to a second end 1916 of the first portion 1911 a of the outercoil 1911, at the opposite side of the coil 1911, namely, at about 180°with respect to any of connections 1940, 1945, or 1955. The second end1925 of inner conductor 1920 is connected to a second end 1912 of thesecond portion 1911 b of the outer coil 1911 at the opposite side of thecoil 1911 along the axis X-X, namely, at about 180° with respect to anyof connections 1940, 1945, or 1955.

The current i(t) flowing through active leads 228 a produces a firstmagnetic field 1905 proportional to the rate of change of the sensedcurrent i(t). The outer coil 1911 detects the first magnetic field 1905and produces a first voltage corresponding to the first magnetic field1905. The outer coil 1911 also detects a second magnetic field 1930 andproduces a second voltage corresponding to the second magnetic field1930. The second magnetic field 1930 is orthogonal to the first magneticfield 1905 and is not related to the sensed current. The inner conductor1920 senses the second magnetic field 1930 and produces a third voltagecorresponding to the second magnetic field 1930. The second voltage andthird voltage have approximately the same magnitude and are removedthrough conditioning circuitry 1976.

A fourth voltage occurs at the first connection 1945 due to capacitivecoupling of the active lead 228 a and is approximately the same becausethe Rogowski coil 1900 is symmetric. The fourth voltage is removed bythe operational amplifier 1960 as a common mode voltage to attain thefirst voltage which is indicative of the current i(t).

The conditioning circuitry 1976 includes operational amplifier 1960 andtwo filters 1972 a, 1972 b. The first portion 1911 a of the outer coil1911 is connected to the negative terminal 1962 of the operationalamplifier 1960 via a first resistor 1950 a. The second portion 1911 b ofthe outer coil 1911 is connected to the positive terminal 1964 of theoperational amplifier 1960 via another first resistor 1950 b. The firstresistors 1950 a or 1950 b may be from about 1 kΩ to about 1,000 kΩ. Theoperational amplifier 1960 amplifies and integrates the voltage receivedfrom connections 1945 and 1955 and supplies differential output shown asoutputs 1966 a and 1966 b. Filters 1972 a and 1972 b are connected inparallel to operational amplifier 1960. The filters 1972 a and 1972 bmay be RC filters each including second resistors 1970 a, 1970 b andcapacitors 1980 a, 1980 b in parallel, respectively. The second resistor1970 a, 1970 b may be from about 33 kΩ to about 3330 kΩ and thecapacitor may be from about 1 nF to about 100 nF.

Both portions 1911 a and 1911 b of the outer coil 1911 have an air coreor any other suitable core material, which provides a low inductancewithin the outer coil 1910. The impedance between the positive input1964 or negative input 1962 of the operational amplifier 1960 is equalto about two times the first resistors 1950 a, 1950 b and is balanced.The inductance of coil 1900 may be calculated using Formula II(described above). As the load impedances are in parallel, thenimpedance of the coil is the dominant impedance since the coil 1900 hasthe lowest impedance. Further, the impedance of the symmetric coil 1900is about half the coil 1936.

Above described embodiment of coil 1911 of FIG. 19B may be implementedon a printed circuit board (PCB). FIG. 20 is a top view of a symmetricprinted Rogowski coil 2000 disposed on a PCB 2005 with opening 2010.Opening 2010 is of sufficient size to allow active lead 228 a to passthrough, but also small enough to maintain active lead 228 aapproximately in the center for the Rogowski coil 2000. Alternatively, asymmetric fixture (not shown) may be used to attach the active lead 228a to the printed Rogowski coil 2000 and center the active lead 228 awithin the printed Rogowski coil 2000. In another alternative, theactive lead 228 a may be a rigid conductor that goes between a firstcircuit PCB below (not shown) and a second circuit PCB (not shown) abovethe printed Rogowski coil 2000 on PCB 2005 through opening 2010. The PCB2005 and the first and second PCBs s then include mounting holes and afixture (not shown) to hold the each PCB parallel in a stackarrangement.

Similar to FIGS. 5-6, the symmetric Rogowski coil 2000 includes toplines 2030 printed on the top side of the PCB 2005 and bottom lines 2040printed on the bottom side of the PCB 2005 connected together with vias2020. The vias 2020 extend completely through the PCB 2005. Anintentional gap 1927 is formed at a discontinuity between connections1915 and 1925 because vias 2020 extend completely through PCB 2005,which does not allow connections 1915 and 1920 to each connect to innerconductor 1920 in the same x-y location.

FIG. 21 is a top view of an alternative symmetric Rogowski coil 2100disposed on PCB 2005. Vias 2120 are buried vias and connect internallayers without being exposed on either surface of the PCB 2005. Theouter coil 1911 is printed on two outer layers 2130, 2140 of the PCB2005 and connected together with buried vias 2120. The inner conductor1920 is printed on a third layer 2150, which is between layers 2130 and2140. Inner conductor 1920 connects separately to first portion 1911 aand to the second portion 1911 b of the outer coil 1911 via connection2110. Connection 2110 is a buried via and provides for the innerconductor 1920 to connect to each portion 1911 a, 1911 b of the outercoil 1911 at the same x-y location.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A current sensor configured to measure an ACcurrent of a first conductor, the current sensor comprising: an outercoil including with a first portion and a second portion, wherein eachof the first and second portions are disposed about the first conductorpassing through a center of the outer coil; and an inner conductordisposed within the first and second portions of the outer coil andconnected to each of the first and second portions of the outer coil. 2.The current sensor according to claim 1, further comprising: aconditioning circuit including a first connector coupled to the firstportion of the outer coil and a second connector coupled to the secondportion of the outer coil, wherein the conditioning circuit isconfigured to amplify and integrate a voltage received from the firstand second connections and to output a measured AC current of the firstconductor.
 3. The current sensor according to claim 1, wherein the firstand second portions are separated by a gap which and the inner conductorcomprises a connector connecting the inner conductor to ground, suchthat the gap and the connector define an axis and the current sensor issymmetrical about the axis.
 4. The current sensor according to claim 3,wherein the inner conductor is connected to ground at approximately 0°relative to the locations of the first and second connections along theaxis.
 5. The current sensor according to claim 4, further comprising aninductance at the outer coil is equal to about half of the inductance ofthe outer coil.
 6. The current sensor according to claim 3, wherein theinner conductor is connected to a second end of the first portion of theouter coil approximately 180° relative to the locations of the first andsecond connections along the axis.
 7. The current sensor according toclaim 3, wherein the inner conductor is connected to a second end of thesecond portion of the outer coil approximately 180° relative to thelocations of the first and second connections along the axis.
 8. Thecurrent sensor according to claim 1, wherein the conditioning circuitincludes an amplifier including a first input configured to connect tothe first connection and a second input configured to connect to thesecond connection.
 9. The current sensor according to claim 8, whereinthe first and second connections generate a fourth voltage.
 10. Thecurrent sensor according to claim 7, wherein the conditioning circuitfurther includes at least one filter connected to at least one of theamplifier or the first and second connections.
 11. The current sensoraccording to claim 1, wherein the first second portions of the outercoil are configured as a single coil with a center tap configured toconnect the inner conductor to the outer coil.
 12. An electrosurgicalgenerator, comprising: a radio frequency output stage configured tooutput at least one radio frequency waveform through an active lead; anda current sensor coupled to the output stage and configured to output afirst differentiated signal corresponding to a current of the at leastone radio frequency waveform, the current sensor coupled to a firstconditioning circuit configured to integrate the first differentiatedsignal to output a processed current signal indicative of the current,wherein the current sensor is symmetrical about a horizontal line andincludes: an outer coil including a first portion and a second portion,wherein each of the first and second portions form half of a toroidabout the active lead, which is disposed through a center of the outercoil; an inner conductor disposed within the first and second portionsof the outer coil; and a voltage sensor coupled to the output stage andconfigured to output a second differentiated signal corresponding to avoltage of the at least one radio frequency waveform, the voltage sensorcoupled to a second conditioning circuit configured to integrate thesecond differentiated signal to output a processed voltage signalindicative of the voltage, wherein the first and second conditioningcircuit have a substantially similar bandpass and phase response. 13.The electrosurgical system according to claim 12, wherein the outer coiland the inner conductor are disposed on a printed circuit board with theactive lead passing through the outer coil.
 14. The electrosurgicalsystem according to claim 13, wherein the printed circuit boardcomprises: outer conductive traces coupled around the active lead, theouter conductive traces interconnected by at least one via through theprinted circuit board.
 15. The electrosurgical system according to claim14, wherein the outer coil comprises: a plurality of top conductivetraces disposed on a top dielectric layer of the printed circuit board;a plurality of bottom conductive traces disposed on a bottom dielectriclayer of the printed circuit board, wherein the outer conductive tracesare disposed over the bottom and top dielectric layers; and a pluralityof inner and outer vias interconnecting the pluralities of top andbottom conductive traces to form the outer coil.
 16. The electrosurgicalsystem according to claim 14, wherein the inner conductor comprises: atleast one conductive trace disposed within the outer coil and printed onan intermediate dielectric layer between the top and bottom dielectriclayers of the printed circuit board.